The treatment of injuries to the spine has advanced significantly, including treatment for many forms of spinal injury and deformities that can occur due to disease, congenital effects, the effects of tumors, and, of course, fractures and dislocations attributable to physical trauma. For many years, the use of elongated rigid plates has been helpful in the stabilization and fixation of the spine.
It has been found that many plate designs allow for a uni-cortically or bi-cortically intrinsically stable implant. It has also been found that fixation plates can be useful in stabilizing the upper or lower cervical spine in traumatic, degenerative, tumorous or infectious processes. Moreover, these plates provide the additional benefit of allowing simultaneous neural decompression with immediate stability.
During the many years of development of cervical plating systems, particularly for the anterior approach, various needs for such a system have been recognized. For instance, the plate must provide strong mechanical fixation that can control movement of each vertebral motion segment in six degrees of freedom. The plate must also be able to withstand axial loading in continuity with each of the three columns of the spine. The plating system must be able to maintain stress levels below the endurance limits of the material, while at the same time exceeding the strength of the anatomic structures or vertebrae to which the plating system is engaged.
Another recognized requirement for a plating system is that the thickness of the plate must be small to lower its prominence, particularly in the smaller spaces of the cervical spine. The screws used to connect the plate to the vertebrae must not loosen over time or back out from the plate. Preferably the plate should be designed to contact the vertebrae for greater stability.
On the other hand, while the plate must satisfy certain mechanical requirements, it must also satisfy certain anatomic and surgical considerations. For example, the cervical plating system must minimize the intrusion into the patient and reduce the trauma to the surrounding soft tissue. It has also been found that optimum plating systems permit the placement of more than one screw in each of the instrumented vertebrae.
Many spinal plating systems have been developed in the last couple of decades that address some of the needs and requirements for cervical fixation systems. One example is the Anterior Cervical Plating System disclosed in U.S. Pat. No. 6,152,927, which is hereby incorporated by reference. However, even with the more refined plating system designs, there still remains a need for a spinal plating system that provides a high quality, durable device with modulus and mechanical strength properties similar to that of cortical bone. Metallic implants, with a substantially higher modulus than cortical bone, can cause a phenomenon known as “stress shielding,” which is commonly thought to lead to bone mass loss and the loosening and subsequent failure of some metallic orthopedic implants. Additionally, radiographic qualities of metallic implants often produce imaging artifacts and scatter, which hinder the inspection of bone growth when using conventional imaging via X-ray, CAT scanning, or MRI techniques.